If any city in the world is a migrant's city, it is this city, which is why it is a showcase of the future. According to the United Nations, more than half the world's population is now living in cities for the first time in history, as people move for jobs, education, and better services. By 2050, 70 percent of the world's population is expected to be urbanized.

This demographic shift poses challenges: creating new slums, overwhelming governments, and placing new demands on land and water. But most observers say the gloom-and-doom scenarios of the 1980s and '90s, in which cities were predicted to collapse and, as one expert put it, resemble the set of the darkly futuristic movie "Blade Runner," have given way to a sense of optimism. Governments, NGOs, and the migrants themselves, they say, are showing resilience in adapting to a more urbanized world.

"The cities are more crowded than ever. The problems are probably worse today.... But there is less of a sense of hopelessness now," says Robert Engelman, vice president for programs at the Worldwatch Institute in Washington, D.C. and author of "More: Population, Nature, and What Women Want."

"There has not been a passive response. There are innovative ways that people have learned how to deal with the problems."

On a recent day, a group of indigenous women participated in a workshop to develop leadership skills – a crucial component to one day becoming business owners, says CARE, the Atlanta-based NGO, which, among other things, helps poor women set up micro-businesses. All these women moved to El Alto – some from the highlands, some from the high plains – for a better life. Some relocated recently, others more than 20 years ago. Like most migrants here, their economic status is precarious. Many work as domestic servants or sell items such as soap or socks on street corners.

"The hardest thing is that you get here and everything requires money," says Isabel Aduviri, who is forming a macramé business with other women in this group. Her family of four makes ends meet because her mother still owns land in the countryside and shares the produce. But it was a trade-off she was willing to make. "In the countryside there is nothing," she says.

Latin America and the Caribbean is the world's most urbanized developing region, with 78 percent of residents living in cities. In Bolivia, the urban population grew by a million – from roughly 5 million to 6 million residents – from 1999 to 2006, according to the latest numbers from the national statistics office.

Most move for jobs, like Teodocio Mamani did recently. The farmer who worked the shores of Lake Titicaca his whole life relocated to El Alto and now works nights as a security guard. "We just couldn't make it anymore," he says, looking out at his new neighborhood, where houses under construction are sprawled out across the plains, with the Andes in the background.

But this search for employment challenges cities. Elias Troche, head of economic development for El Alto's municipal government, says they run employment programs for youths – giving them internships to work in the factories that draw so many migrants. "We try to give them hope. But there is a lot we cannot address," he says. When jobs are scarce, violence ensues. "A new migrant comes and it's one more unemployment figure."

Yet Hania Zlotnik, the director of the UN Population Division, says that even if some migrants end up in urban poverty, they tend to be better off in cities than the countryside. In Bolivia, for example, the percentage of those living in poverty in the cities in 2006 was 50 percent; it was over 75 percent in rural areas. "It is true that cities have underemployment and problems, but it is better than staying in rural areas where you don't have anything," says Ms. Zlotnik.

Cecilia Tacoli, a senior researcher with the International Institute for Environment and Development in London, says that governments tend to blame migration on growth of slums and violence, but she says it is misplaced. Providing services such as electricity and water is easier in urban areas than dispersed agricultural ones. And urban migrants tend to have networks of friends and family to help them. "The poorest people do not have the means to go to the city," says Ms. Tacoli.

Many NGOs have shifted their approach – moving away from trying to halt the rural exodus, says Marco Zelada, who manages programs for CARE International in Bolivia. "A few years ago we realized we cannot close our eyes. We have to focus on urban areas."

CARE opened up its first permanent office 34 months ago in El Alto, which was once a suburb of La Paz with 11,000 residents in 1950 and whose population is set to surpass that of the administrative capital. Since CARE opened its office here, says Gustavo Garcia, who heads the El Alto program, the city has grown from 10 to 13 districts. "People keep coming."

Many of those coming are women. In Latin America there is a long tradition of more women moving to cities than men, says Ms. Zlotnik. In Bolivia, while census numbers in El Alto reveal an almost equal ratio of women to men, women tend to migrate more permanently, while men migrate seasonally. Women are also more visible, says Mr. Garcia – holding the majority of jobs on street corners while men tend to work in construction.

This has given women a chance to find their voices. "Migration can empower women," says Norah Quispe, who runs a program to promote gender equality for the organization Gregoria Apaza in El Alto. She says that women migrants are vulnerable, but living in cities gives them access to civic roles they would not have in the countryside.

Yet migration can also challenge networks. "There is something we've lost. There is more money here, but the life isn't as healthy," says Feliza Calle Blanco, who sells sports clothing with the aid of Pro Mujer, a microfinance and women's development network. She and other women who benefit from Pro Mujer tick off the difficulties – infidelity, violence on television, alcohol. She is proud to say that her daughter is planning on attending a university – when she herself only learned how to read in her 20s. "But there are so many drawbacks. Our kids want to imitate foreigners, and feel discrimination for being indigenous," she says. Her sentiments reflect urban malaise that parents from New York City to Nairobi can relate to. "We used to make our own toys, now kids just want to play on the Internet."